How to measure a bike !

[Fred Green]

Hello All,

I am pretty new to the vintage bike world. I always see measurements for bikes and want know how do you measure a bike? Is it by the size of the rims? The size of the vertical bar between the seat and crank? Any help is great. Thanks.

Fred Green
Sparta

 

[fordmike65]

Wheel size (24,26,28") and the actual frame size, usually measured from the center of the crank(bottom bracket) to the top of the seat tube.

 

[Fred Green]

Awesome! That will help get me on the road. Thanks again.

Fred
Sparta

 

[Duchess]

But wheel size is deceiving, so don't assume too much! There are multiple sizes of some wheels of the same listed diameter in inches, 27" is larger than 29", which is actually 700c, a French measuring system . . . Eh, check this out: https://www.sheldonbrown.com/tire-sizing.html

There are also multiple ways to measure frames, but usually you're good with the center of BB to top of seat tube.

 

[Sven]

Measuring the frame

 

[Fred Green]

Hello,

The tube measurement came out to 18 1/2" The wheels are still on the bike with flat old tires on them. I measured directly across the wheel going acoss the axle and got a measurement of 23" That sounded strange for me. The rims are Schwinn tubular S-2 rims Am I on the right track here? I need to dismount the old tubes and tires so I will get another measurement when I get that done. Thanks again.

Fred
Sparta

 

[Roger Henning]

Bicycles unlike cars do not measure the wheel diameter but the outside diameter of the tire. S-2s are probably 26 inch but the also came in 24 and 20 inch sizes. Roger

 

[Fred Green]

Roger,
Thank you. That enlightened my dumbass!! I will get a circumference measurement this evening!

 

[Duchess]

It's not the circumference, it's the diameter of the tire installed on the wheel, which is a really stupid measuring system as any given rim can take a range of tire widths, resulting in different diameters for the same sized rim. By that logic, the 13" wheels on my 80s Subaru was rolling through the hood on 21s, like a donk progenitor. That sounds like you have a 26" rim there as a 1.5" tire height is likely, but if you can read the sidewall of the old tires, that would give you a definite answer.

The best measurement system for tires is ISO as it is based on the actual diameter of the rim in mm and not some arbitrary system, but that's not helpful here as I doubt they have the ISO listed on the sidewall of the tires of the bike you're looking at.

 

[Fred Green]

Thanks again.

Fred
Sparta